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Northward Laramide thrusting in the Quitovac region, northwestern Sonora, Mexico: Implications for the juxtaposition of Paleoproterozoic basement blocks and the Mojave-Sonora megashear hypothesis

By
Alexander Iriondo
Alexander Iriondo
Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA, and U.S. Geological Survey, MS 974, Box 25046, Denver Federal Center, Denver, Colorado 80225, USAPresent address: Centro de Geociencias, UNAM, Campus Juriquilla, C.P. 76230 Juriquilla, Querétaro, México; iriondo@geociencias.unam.mx.
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Luis M. Martínez-Torres
Luis M. Martínez-Torres
Departamento de Geodinámica, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain
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Michael J. Kunk
Michael J. Kunk
U.S. Geological Survey, MS 963, Box 25046, Denver Federal Center, Denver, Colorado 80225, USA
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William W. Atkinson, Jr.
William W. Atkinson, Jr.
Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA
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Wayne R. Premo
Wayne R. Premo
U.S. Geological Survey, MS 963, Box 25046, Denver Federal Center, Denver, Colorado 80225, USA
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William C. McIntosh
William C. McIntosh
New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801, USA
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Published:
January 01, 2005

Restoration of 12%–30% Basin and Range extension allows direct interpretation of ductile fabrics associated with a stack of Laramide thrust faults in the Quitovac region in northwestern Sonora. The inferred direction of displacement of these thrusts varies gradually from N63°W to N23°E and is interpreted to represent a clockwise rotation of the direction of Laramide thrusting through time. The thrust faults represent a piggy-back sequence of thrusting propagating north, toward the foreland. The average direction and sense of displacement of the thrusts is N18°W, and the cumulative 45 km of estimated northward-directed displacement corresponds to ∼86% of shortening.

Based on geochronological constraints, onset of thrusting in Quitovac occurred sometime between 75 and 61 Ma, whereas cessation occurred at ca. 39 Ma. The presence of Paleocene-Eocene orogenic gold mineralization, spatially associated with thrusting, strengthens our idea that compressional tectonism associated with the Laramide orogeny is a very important and widespread dynamometamorphic event in the region.

Similarities in age, kinematics, and structural stratigraphy indicate that the thrusting in the Quitovac region may be equivalent to the Laramide Quitobaquito Thrust in southwestern Arizona. In both areas, thrust faults juxtapose the Paleoproterozoic Caborca and “North America” basement blocks. This juxtaposition was previously proposed as exclusively related to movements along the hypothetical Upper Jurassic Mojave-Sonora megashear. The Laramide northward displacements and clockwise rotations recorded in the Caborca block rocks in Quitovac contradict the southward displacements (∼800 km) and counterclockwise rotations inherent in the left-lateral Upper Jurassic Mojave-Sonora megashear hypothesis. We conclude that if this megashear exists in northwestern Sonora, its trace should be to the southwest of the Quitovac region.

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GSA Special Papers

The Mojave-Sonora Megashear Hypothesis: Development, Assessment, and Alternatives

Thomas H. Anderson
Thomas H. Anderson
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Jonathan A. Nourse
Jonathan A. Nourse
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James W. McKee
James W. McKee
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Maureen B. Steiner
Maureen B. Steiner
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Geological Society of America
Volume
393
ISBN print:
9780813723938
Publication date:
January 01, 2005

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